Front heater core flushed with CLR now producing 135 degree vent heat.

[decoco]

quick question:

Having similar issues with my '92. But a little history first. When we bought it a few years ago in November and parked it until spring, we discovered a busted rad and block in the spring. It was my bad for not checking when we bought it, but the previous owner only had straight water in the system and no thermostat, and after a harder winter with temps well below freezing those parts let loose. The engine still ran just fine as it was an external crack, but we had to add fluid every other day or so. When we changed the rad and installed a t-stat we noticed how dirty the "coolant" was, so I flushed the system and got what looked like straight mud out. Took about 4 flushes to run clear. Then we swapped in a 2FE. That was about 3400 miles ago. Everything has been running good and good heat out of heaters.

Now this winter has been extra cold and I noticed a few weeks ago the rear heater was not producing any heat until after about 30 mins and some uphill driving, and even then it would go lukewarm after a minute. Just today the front heater started running cold, it didn't do that last time I ran it, and it's been cold outside for awhile. Engine temps on the dash gauge come up to normal right away and don't fluctuate. I suspected t-stat, but the hose on the rad side of t-stat was nice and hot and the rad had pressure when I burped the cap, so I'm thinking the t-stat is good. Heater valve on firewall appears to be functioning properly. So I'm left with thinking the cores are plugged, and rather quickly.

Will have to do the flushes as mentioned here on the site, but would like to use something stronger than CLR. So one question I have is does anyone know what the heater cores are made of? If copper or brass, then that is good. But is any aluminum, then not good. Reason why, is I have flushed old (like early 70's old) FJ40 cores that are brass with straight muriatic acid. Muriatic eats aluminum, but not brass or copper, and does a terrific job of cleaning plugged cores with hard deposits. Had a core once that was over 75% plugged, came out like new after 3 flushes with muriatic.

quick question, do you hear any air pockets in your dash when you rev up your engine?
Is there any chance you may a hose leaking? - low heating temperature may be a symptom of you loosing coolant somewhere and not enough pressure/circulation in the system to warm up your system as needed. I'm almost pointing at the rear heater hoses based on your description.

 

[decoco]

I have a related/unrelated question for you folks in the cold.

When it's cold as hell I sometimes get a high pitched whirring sound from the passenger side associated with the hvac/fan speed. I'm assuming it's the blower motor? does this sound right, if so should I be looking to have one as a spare just in case or is this normal?

 

[izzyandsue]

Passenger side, behind the glove box is the fan. It is a simple one to remove and clean out debris that can accumulate for years. There was a post here recently, someone was just doing that and removing what seemed like a bird's nest from the fan. So yes, debris can get accumulated and throw the fan off some and make noise, removal and cleaning should cure it. I am overdue on mine too.

 

[Bambusiero]

Be aware - You can get an air lock condition that totally prevents any heat output, even when the system is in fine condition.

Not long ago I did a full radiator flush procedure, just for preventative maintenance.
Basically, drain, fill, run until full heat is felt - multiple times, to dilute the previous residual whatever.
So, already knew for sure the heater cores are flowing fine.
On the last fill cycle - no heat. Waiting, running, waiting, checking heater valve, revving, waiting - nothing...WTF?
Just had to pull the top heater valve hose and let some coolant gush out.
Back together and got heat fast!

I've done the exact same thing dozens of times. Never had this happen before.